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astro Flashcards

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1
Q

what is one light year

A

the distance that light travels in one year in a vacuum
9.46x10^15 m

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2
Q

what is parallax

A

apparent shift in relative position of two objects due to the changing position of the observer

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3
Q

what is the astronomical unit (AU)

A

the mean distance between the Earth and the sun
is 1.50 x 10^11 m

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4
Q

what is the parsec

A

A unit of distance that gives a parallax angle of 1 second of an arc (of a degree), using the radius of the Earth’s orbit (1 AU) as the baseline of a right–angled triangle

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5
Q

what is the hipparcos scale

A

scale which tells you the brightness of a star

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6
Q

what magnitudes are the brightest and dimmest stars

A

brightest are magnitude 1
dimmest are magnitude 6

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7
Q

what magnitude is used in hipparcos scale

A

apparent magnitude

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8
Q

what is apparent magnitude

A

how bright a star appears from earth

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9
Q

why was the apparent magnitude system formalised

A

our eyes have logarithmic response to light

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10
Q

how many times brighter is magnitude 1 than magnitude 6

A

100 x

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11
Q

how many times brighter is a magnitude brighter than the previous

A

100^1/5
2.51

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12
Q

are we able to observe magnitudes lower than 6 and negative magnitudes

A

yes

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13
Q

what is luminosity

A

the total power output of a star
measure is watts

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14
Q

what is apparent magnitude

A

apparent magnitude being measured from a distance of 10 pc

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15
Q

distance modulus equation

A

m - M = 5 log (d/10)

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16
Q

what is a blackbody

A

an idealised emitter and absorber of radiation (object that absorbs all radiation and emits radiation over a continuous range of wavelengths)

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17
Q

what is the area under a black body curve

A

total energy radiated per unit of time per unit of surface area by the object at that temperature

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18
Q

what do you have to remember when drawing black Body curve diagrams

A

The left hand side must be drawn steeper than the right hand side
The intensity must decrease towards (but not reach) zero as the wavelength increases.
The line must not cross the intensity axis (y-axis)

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19
Q

what is peak wavelength determined by for a black body

A

temperature

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20
Q

what is weins displacement law

A

λmaxT=2.9×10−3m⋅K

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21
Q

what is weins law used for

A

to find the surface temperature of the star

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22
Q

stefan boltzman law describes

A

The temperature of a blackbody and the amount of energy it radiates

23
Q

what is stefan Boltzmann law

A

P=σAT^4
σ = 5.67×10−8Wm−2K−4
A = 4πr^2

24
Q

what does energy flux or surface flux show

A

shows energy leaving the star

25
Q

what is the energy flux or surface flux of the star

A

P=σT^4

26
Q

what happens when photons are absorbed by electrons in a cool gas

A

a dark line is created in an continuous spectrum

27
Q

what is the order of the hydrogen Balmer lines

A

O B A F G K M

28
Q

what is the temperature range for O

A

25,000 - 50,000

29
Q

what is the temperature range an the strongest absorption lines for B

A

11,000 - 25,000
He H

30
Q

what is the temperature range an the strongest absorption lines for A

A

7,500 - 11,000
H

31
Q

what is the temperature range an the strongest absorption lines for F

A

6,000-7,500
ionised metals

32
Q

what is the temperature range an the strongest absorption lines for G

A

5000 - 6000
ionised and neutral metals

33
Q

what is the temperature range an the strongest absorption lines for K

A

3,500 - 5,000
neutral metals

34
Q

what is the temperature range an the strongest absorption lines for M

A

less than 3,500
neutral atoms, TiO

35
Q

what is on the axis of HR diagram

A

spectral class or temp on the x axis
and absolute magnitude or luminosity on the y axis

36
Q

where is the main sequence on the HR graph

A

absolute magnitude from -10 to 15
spectral classes O to M
shape squiggly line from left to right

37
Q

where is super giants on the HR graph

A

absolute magnitude from -5 to -10
spectral classes A to end of M
shape oval

38
Q

where is giants on the HR graphs

A

absolute magnitude of zero
spectral classes start of g to end of M
shape oval

39
Q

where is white dwarfs on HR graph

A

absolute magnitude between 10 15
spectre class between B
shape oval

40
Q

length of axis on HR diagram

A

-10 to 15 y axis
O to M

41
Q

how are stars born

A

out of nebulae. the gravitational forces pull at the gas compressing it forming protostar. GPE Turns into thermal energy so interior becomes hotter and hotter. there’s fusion of hydrogen to form helium, fusion reactions cause the outer layers of protostar to become hot and a light emitting layer and protostar becomes star

42
Q

what is a nebula

A

interstellar cloud of gas

43
Q

what is a protostar

A

making of a star

44
Q

what happens once new star is formed

A

star reaches internal equilibrium as inward gravitation attraction is balanced by outward radiation pressure, star becomes stable with constant luminosity.and joins the main sequence according to its mass

45
Q

where does a star spend most of its time

A

main sequence

46
Q

when does a star become a supergiant or a giant

A

when most of the hydrogen has been converted to helium so core collapses on itself and so outer layers of star expand and cool so star swells out and becomes super giant or giant

47
Q

when does red giant become white dwarf

A

when nuclear fusion in the core of star stops the star cols off and the core contracts causing the outer layers to be thrown off. outer layers thrown off as shells of hot gas forming a planetary nebula

48
Q

why is supernova called a supernova

A

because the event is brighter than a nova (new star) in the same galaxy

49
Q

what is a neutron star

A

core of a supernova after all surrounding matter has been thrown off into space

50
Q

what is a black hole

A

object so dense that not even light can escape it

51
Q

why is a black hole so dense

A

because escape velocity is above the speed of light

52
Q

what is the event horizon

A

sphere surrounding the black hole from which nothing can emerge

53
Q

what is the Schwarzschild radius

A

radius of the event horizon

54
Q

equation for Schwarzschild radius

A

R(s) = 2GM/c^2

physics (11 decks)

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